Java,空指针异常.当我向数组添加一个对象时

Question

我是java的新手,我正在尝试将对象添加到对象数组中.我有2个班级,银行和帐户.Bank包含一组Accounts对象.

Bank构造函数初始化Accounts数组.

public Bank (String bankName, int num) {

        nameOfBank = bankName;
        max = num;
        Account[] accounts = new Account[max];
        count = 0;

这是我的addAccount方法.

public boolean addAccount (Account acct) {
        if(acct == null) {
            return false;
        }

        accounts[count++] = acct;
        return true;
    }

这是我在main中添加帐户的方式

newBank.addAccount(test);

PS.我不允许使用除java数组以外的任何东西.(没有arrayList)

Exception in thread "main" java.lang.NullPointerException
        at Bank.addAccount(Bank.java:55)
        at TestBank.main(TestBank.java:15)

Answer 1

您已将其定义accounts为构造函数的局部变量,而不是类级别成员.

public class Bank {
    Account[] accounts;
    int count;

    public Bank(String bankName, int num) {
        accounts = new Account[num];
        count = 0;
    }

    public boolean addAccount(Account acct) {
        // Do your work
    }
}